Make MAKE-LISP-OBJ pickier on CHENEYGC.

  * Move the valid_lisp_pointer_p() guts from gencgc.c to
gc-common.c, updating header files and staticness as required.
Also remove all of the debug output conditional on
gencgc_verbose (which is obviously gencgc-specific).

  * Make the lisp-side VALID-LISP-POINTER-P not-gencgc-specific.

  * Always use VALID-LISP-POINTER-P in MAKE-LISP-OBJ instead of
using some simple bounds-check on CHENEYGC.